--- title: "Greenhouse gases, effects and CO2-equivalent calculation" subject: "Environment and Pollution Control" chapter: 7 key: "semester_7/environment_and_pollution_control:greenhouse-gases-causes-effects-co2e" source: https://www.bctengineer.com/q/semester_7/environment_and_pollution_control/greenhouse-gases-causes-effects-co2e site: BCT Engineering --- # Greenhouse gases, effects and CO2-equivalent calculation Environment and Pollution Control · Chapter 7: Global issues and responsible development practices - Asked in: year not given, 3+3 marks - Video: [What does carbon dioxide equivalent mean? | Climate Now Mini Video 5](https://www.youtube.com/watch?v=NzZSZForZh8) — Climate Now - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/environment_and_pollution_control/greenhouse-gases-causes-effects-co2e - Whole chapter: https://www.bctengineer.com/md/semester_7/environment_and_pollution_control/chapter-7 ## Question (a) Explain the greenhouse effect and the causes of increase of the greenhouse gases. Describe the effects of global warming. (b) Burning 1 tonne of coal containing 75% carbon releases how much CO2? A landfill releases 100 tonnes of methane; find its CO2-equivalent using a 100-year global warming potential (GWP) of 28 for methane. ## Short answer Greenhouse gases absorb infrared radiation and warm the Earth; increased CO2, methane, and nitrous oxide from fossil fuels, agriculture, and landfills cause global warming, melting ice, sea-level rise, and extreme weather. Burning 1 tonne of coal with 75% carbon releases 2.75 tonnes CO2; 100 tonnes methane equals 2800 tonnes CO2e using GWP 28. ## Answer #### (a) Greenhouse effect Short-wave solar radiation passes through the atmosphere and warms the earth. The earth re-emits long-wave infrared radiation, and greenhouse gases (GHGs) absorb part of it and send it back, keeping the earth about 33 $^\circ$C warmer (average 15 $^\circ$C instead of $-18\ ^\circ$C). This natural effect is essential for life; the problem is the **enhanced greenhouse effect** due to rising GHG levels. ```text Sun --short-wave--> | atmosphere (CO2, CH4, N2O, H2O) | ^ absorbs and re-radiates Earth --long-wave IR---+----> part escapes to space ``` **Main GHGs and causes of increase:** | Gas | Main anthropogenic sources | GWP (100 y) | |---|---|---| | Carbon dioxide | Fossil fuel burning, cement, deforestation | 1 | | Methane | Rice fields, cattle, landfills, coal and gas leaks | 28 | | Nitrous oxide | Fertilizers, biomass burning, industry | 265 | | CFCs, HFCs, $\text{SF}_6$ | Refrigeration, aerosols, foams | thousands | | Ozone (tropospheric) | Vehicle smog | - | Atmospheric $\text{CO}_2$ has risen from about 280 ppm before industrialisation to above 420 ppm today because of fossil fuels and deforestation. **Effects of global warming:** rise in global temperature, melting of glaciers (serious for Himalayan glaciers and rivers) and polar ice, sea-level rise, more floods, droughts and extreme weather, glacial lake outburst floods (GLOF), threat to food production, spread of vector-borne diseases, loss of biodiversity, ocean acidification. #### (b) Numerical Reaction: $\text{C} + \text{O}_2 \rightarrow \text{CO}_2$, mass ratio $44/12$. Carbon in coal $= 0.75\times1\ \text{t} = 0.75$ t. $$ m_{\text{CO}_2} = 0.75\times\frac{44}{12} = 2.75\ \text{t} $$ Methane CO$_2$-equivalent: $$ \text{CO}_2\text{e} = 100\ \text{t}\times28 = 2800\ \text{t CO}_2\text{e} $$ **Answer: 1 t of coal gives 2.75 t of CO$_2$; 100 t of methane is equal to 2800 t CO$_2$e.** ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What does the natural greenhouse effect do? A. GHGs absorb part of the earth's long-wave IR and send it back, keeping earth about 33 degC warmer B. GHGs block incoming sunlight C. GHGs cool the earth to -18 degC D. Only ozone traps heat Answer: A. Short-wave sunlight passes in; GHGs absorb outgoing long-wave IR, giving average 15 degC instead of -18 degC. (Key point: Natural greenhouse effect) 2. 1 t of coal with 75% carbon burns completely. How much CO2 is released? A. 0.75 t B. 2.75 t C. 1.65 t D. 3.67 t Answer: B. Carbon 0.75 t x 44/12 = 2.75 t CO2. (Key point: CO2 from coal) 3. 100 t of methane with GWP 28 equals how much CO2e? A. 28 t B. 128 t C. 2800 t D. 3.57 t Answer: C. CO2e = mass x GWP = 100 x 28 = 2800 t. (Key point: CO2 equivalent) 4. Which is a particular concern of global warming for Nepal? A. Himalayan glacier melt and glacial lake outburst floods B. Loss of the ozone layer from CO2 C. Reduced CO2 levels D. Lower sea level Answer: A. Melting Himalayan glaciers affect rivers and cause GLOF, besides floods, droughts and sea-level rise elsewhere. (Key point: Effects of warming) ## Related in Environment and Pollution Control - [Landfill volume and area calculation](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Alandfill-area-volume-numerical) — Environment and Pollution Control, chapter 5 - [Sources and effects of SO2, NOx and CO](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Agaseous-pollutants-so2-nox-co) — Environment and Pollution Control, chapter 1 ## Related in other subjects - [Global warming and greenhouse gases](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Aglobal-warming-ghg-climate) — Energy Environment and Society, chapter 4 - [Greenhouse gases and global control efforts](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Agreenhouse-gases-efforts) — Engineering Chemistry, chapter 3 - [Global warming: meaning, causes, consequences](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aglobal-warming-causes-consequences) — Engineering Chemistry, chapter 3 - [Global warming: causes, consequences, remedies](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aglobal-warming) — Engineering Chemistry, chapter 3, asked 2×